In the September issue of Smithsonian magazine, we see how archaeologists can explore underground without digging it up. Vince Gaffney heads a project that has given us a sort of three-dimensional map of what’s underneath the land surrounding the most mysterious place in Britain: Stonehenge.

Gaffney’s latest research effort, the Stonehenge Hidden Landscapes Project, is a four-year collaboration between a British team and the Ludwig Boltzmann Institute for Archaeological Prospection and Virtual Archaeology in Austria that has produced the first detailed underground survey of the area surrounding Stonehenge, totaling more than four square miles. The results are astonishing. The researchers have found buried evidence of more than 15 previously unknown or poorly understood late Neolithic monuments: henges, barrows, segmented ditches, pits. To Gaffney, these findings suggest a scale of activity around Stonehenge far beyond what was previously suspected.